1. Field of the Invention
This invention relates to haze-free tin oxide coatings, and more particularly, to a method of making such coatings by interposing an improved undercoat film between the substrate and the tin oxide coating.
2. Description of the Invention
There is a demand for glass products, in particular, flat glass, having a tin oxide coating of high optical quality which modifies the radiation transmitting characteristics of the product but causes little or no diffusion of transmitted light. Any significant amount of light diffusion within a transmitted product is apparent as haze, which is detrimental in commercial use.
In the prior art it is recognized that the appearance of haze in tin oxide coatings formed on glass by exposure to tin compounds can be prevented or reduced by application of an intervening coating of suitably selected composition. For example, U.S. Pat. No. 2,617,741 proposes to provide a protective layer preceding the formation of the tin oxide coating by spraying the heated glass with a saturated or relatively concentrated aqueous solution of a suitable soluble metal salt, particularly the acetates of copper, aluminum, lead, zinc, iron, nickel, cobalt, thallium, silver or titanium.
Similarly, Terneu in U.S. Pat. No. 4,329,379, describes an undercoat of a metal oxide formed by decomposition of the acetylacetonate of titanium, nickel or zinc on which a tin oxide overcoat free from perceptible haze can be formed.
Gordon, in U.S. Pat. Nos. 4,187,336 (and 4,206,252) uses a tin oxide coating to provide a non-iridescence on glass structure which is described as being free of visible haze. In this structure, the haze which ordinarily would appear in the tin oxide coating is reduced by first depositing on the window glass an amorphous layer of SiO.sub.2, Si.sub.3 N.sub.4, GeO.sub.2, Al.sub.2 O.sub.3, or silicon oxy-nitride, or mixtures thereof with each other, or with other metal oxides. However, Gordon states that if this layer contains a large proportion of the metal oxides, Ga.sub.2 O.sub.3, ZnO, In.sub.2 O.sub.3, or SnO.sub.2, then haze formation is likely.
U.S. Pat. Nos. 4,547,400 and 4,548,836 describe the use of an undercoat of tin oxide formed from a chlorine-free organic/tin ion-containing compound on which a haze-free doped tin oxide layer can be formed.
The art also recognizes the advantage of using certain tin compounds such as monobutyltin trichloride as a precursor for the tin oxide coating. However, many of these tin compounds will produce hazy coatings unless formed under very restrictive and disadvantageous deposition conditions.
Accordingly, it is an object of this invention to provide an improved method of making haze-free tin oxide coatings.
Another object of this invention is to form a haze-free, tin oxide overcoat on glass from a precursor tin compound under a wide range of deposition conditions.
A specific object herein is to form a haze-free conductive tin oxide by using an improved undercoat film between the glass and the tin oxide coating.
A feature of the invention is the use of a haze-free tin oxide undercoat film on which haze-free tin oxide coatings may be formed.
A particular feature of the invention is the use of monophenyltin trichloride to form a haze-free tin oxide undercoat on glass, and, on which haze-free, conductive tin oxide coatings may be formed from tin compounds under process conditions which ordinarily would give hazy coatings if deposited directly on glass.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.